Dark Devotion. Zathus has advantage on saving throws against being charmed or frightened.

Multiattack. The necromancer makes three Arcane Burst attacks.

Arcane Burst. Melee or Ranged Spell Attack: +6 to hit, reach 5 ft. or range 120 ft., one target. Hit: 25 (4d10 + 3) necrotic damage.

Spellcasting. The necromancer casts one of the following spells, using Intelligence as the spellcasting ability (spell save DC 14, +6 to hit):

Cantrips (At will): Fire Bolt +6 to hit, range 120 ft., one target. Hit: 16 (3d10) fire damage, Light, mage hand, prestidigitation

1st Level (4 slots): Detect Magic, Shield, mage armor, Magic Missile Hit: 11 (3d4+3) force damage

2nd Level (3 slots): Misty Step, Suggestion

3rd level (3 spots): Counterspell, Fireball range 60 ft.. 20ft. radius. Hit: 28 (8d6) fire damage, Fly

4th level (3 spots): Blight range 30 ft., one target. Hit: 36 (8d8) necrotic damage, Greater Invisibility

Summon Undead (1/Day). The necromancer magically summons five skeletons or zombies. The summoned creatures appear in unoccupied spaces within 60 feet of the necromancer, whom they obey. They take their turns immediately after the necromancer. Each lasts for 1 hour, until it or the necromancer dies, or until the necromancer dismisses it as a bonus action.